The grades on a math midterm at Gardner Bullis are normally distributed with $\mu = 75$ and $\sigma = 5.5$. Tiffany earned a n $89$ on the exam. Find the z-score for Tiffany's exam grade. Round to two decimal places.
A z-score is defined as the number of standard deviations a specific point is away from the mean We can calculate the z-score for Tiffany's exam grade by subtracting the mean $(\mu)$ from her grade and then dividing by the standard deviation $(\sigma)$ $ { z = \dfrac{x - {\mu}}{{\sigma}}} $ $ { z = \dfrac{89 - {75}}{{5.5}}} $ ${ z \approx 2.55}$ The z-score is $2.55$. In other words, Tiffany's score was $2.55$ standard deviations above the mean.